Circuits for generating saw tooth oscillations



Dec. 16, 1952 K. G. HUNTLEY 2,622,227

CIRCUITS FOR GENERATING SAW TOOTH OSCILLATIONS Filed Nov. 21, 1950 haven 2v KEITH GORDON HUNTLEY A ffa/wey Patented Dec. 16, 1952 CIRCUITS FOR -GENERATING SAW TOOTH OSCILLATIONS Keith Gordon Huntley, Harlington, Hayes, England, assignor to Electric & Musical industries Limited, Hayes, England, :acompany of Great Britain Application November 21, 1950, Serial 'No. 196,780 In .Great Britain November 30, 1949 I 2 Claims. This finventionrelates to circuits for the generation of electrical sawtooth oscillations in an inductive load and it relates particularly but not exclusively to circuits for generating sawtooth oscillations in the scanning coils of a cathode ray tube incorporated, for example, in television apparatus.

In one form of circuit for this purpose an electron discharge tube (hereinafter referred to-fior rent oscillations in said load, and :a damper tube for reducing undesired oscillations at the ends convenience as the power tube) is arranged to of the short :flanks .ofsa'id sawtooth oscillations, apply a voltage periodically to the load, for exsaid power tube .being coupled to said load Mia ample the scanning coils of a cathode ray tube, two transformers connected in cascade and :the to develop the long flanks of sawtooth current anode-cathode path of said damper tube being oscillations, thetube being rendered nonconductconnected across the connected windings of said ing periodically at times corresponding to the transformers. ends of the long flanks, whereupon a half cycle In order that the saidinvention may rhe :clearly of free oscillation in said coils produces the short understood and readily carried into effect, the flanks of the sawtooth current oscillations. Unsame will now be more fully described with referdesirable free oscillations tend to persist after ence to the accompanying drawing, the single the ends of said short flanks, and accordingly a figure of which shows one form of circuit accordfurther electron discharge tube (hereinafter reing to the invention which is suitable for feeding ferred to for convenience as the damper tube) a sawtooth current to the scanning coils of a is associated with the load, the damper tube becathode ray tube employed in television apparaing non-conducting during the half cycle of free tus. oscillation corresponding to the short flank of Referring to the drawing, reference numeral the sawtooth oscillation and becoming conductl indicates low inductance scanning coils of a ing at the end of the half cycle so as to damp cathode ray tube, sawtooth current being fed to the free oscillations. said coils from a, power tube 2. The power tube It is frequently required to employ a load hav- 2 is coupled to the coils I via two transformers ing a relatively low inductance, this being the 3 and 4 connected in cascade, the anode of tube case, for example, when the load comprises scan- 2 being connected to one end of the primary windning coils, since these are difficulties associated ing of transformer 3, the other end of said windwith the use of high inductance coils. However, ing being connected to the positive H. T. terminal when a low inductance load is employed the 8 and to ground via a blocking condenser 5. One damper tube cannot be connected directly across end of the secondary winding of transformer 3 the load since its impedance relative to that of is connected to one end of the primary winding the load is too great for effective operation of the of transformer 4, and the other ends of said damper tube. It has been proposed to overcome se ondary nd prim ry wind n s re onn cte this difficulty by connecting the damper tube to u t Se y Winding 0 t e transacross a tertiary winding of a transformer via former 4 being connected to the scannin coils l. which the power tube is coupled to the load, so The damper e is ShOWn at 5, and h s its o that a suitably high impedance is presented to cat o pa h c te ac ss the s c dary the damper tube, but such an arrangement has winding of t transformer 3 and the Pr a y the disadvantage that when the damper tube be- Winding 0f the traIlSfOrmer Preferahly the comes conducting the energy which at this time damper tube 6 is provided with a control electrode is stored in the field of the transformer sets up as shown, and a negative feedback path to said ringing oscillations in the circuit comprising the control electrode is p o Via condenser an leakage inductance of the primary and tertiary amplifier being included if desired in the feedwindings and the stray capacities associated back path. The control electrode of the damper therewith, and said ringing oscillations are trans- 5 tube 6 is connected via a resistor 9 to the negaferred to the load due to the leakage inductance tive bias terminal ll]. of the tertiary winding in series with the damper In the operation of the circuit, the power tube tube serving to couple the scanning coils with 2 serves to generate sawtooth current oscillathe circuit in which the ringing oscillations occur. tions in the load I, by virtue of a suitable form The object of the invention is to provide a cirof control voltage applied between the cathode and control electrode of tube 2 by any suitable means. The coils i are of low inductance but the voltage ratio of transformer 4 is arranged to be such, having regard to the type of tube employed as the damper tube, that the impedance presented to the damper tube 6 by the transformer 4 is higher than that of the coils l, and is more suitable than the impedance of coils l for effective operation of the damper tube. Negative feedback is applied to the control electrode of damper tube 6 via condenser I, and serves to reduce the effective resistance of the damper tube, thereby greatly reducing the likelihood of the internal impedance of the damper tube permitting the transfer of ringing oscillations from the leakage inductance circuits of the transformer 3 to the coils l. Negative feedback may also be applied to the control electrode of power tube 2, the feedback tending to improve the linearity of the sawtooth current oscillations in the coils l as described in the United States patent application Serial No. 128,598, filed November 21, 1949 by J. E. Best and R. C. White.

What I claim is:

1. A circuit comprising a low inductance load, a power tube to set up sawtooth current oscillations in said load, a first transformer having its primary winding connected in the output circuit of said power tube, a second transformer havin its primary winding connected to the secondary winding of said first transformer and having its secondary winding connected to said low inductance load, and a damper tube having its anode-cathode path connected across the secondary winding of said first transformer and across the primary winding of said second transformer with said second transformer presenting to said damper tube an impedance higher than that of said load.

2. A circuit comprising a low inductance load, a power tube to set up sawtooth current oscillations in said load, a first transformer having its primary winding connected in the output circuit of said power tube, a second transformer having its primary winding connected to the secondary winding of said first transformer and having its secondary winding connected to said low inductance load, a damper tube having its anode-cathode path connected across the secondary winding of said first transformer and across the primary winding of said second transformer with said second transformer presenting to said damper tube an impedance higher than that of said load, said damper tube having a control electrode, and means for applying negative feedback to said control electrode to reduce the effective resistance of said damper tube.

KEITH GORDON HUNTLEY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,228,266 Gray Jan. 14, 1941 2,230,819 White Feb. 4, 1941 2,251,851 Moore Aug. 5, 1941 2,280,733 Tolson Apr. 21, 1942 2,305,919 Eaton Dec. 22, 1942 2,414,546 Nagel Jan. 21, 1947 2,460,540 Shaw Feb. 1, 1949 

